Pool Filter Waste Setting: What It Does and When to Use It
The short answer
The waste setting sends pool water out the waste line without touching the filter media. Learn when to use it, how to vacuum to waste, and waste vs backwash.
In This Guide
Every multiport valve has a position that sends pool water straight down the drain on purpose. The waste setting bypasses the filter media completely and pumps water out of the pool for good, which makes it the right tool for vacuuming algae and the wrong tool for almost everything else. This guide covers exactly what WASTE does, when to use it, and how to vacuum a pool to waste without draining half your water.
What the Waste Setting Actually Does
On the FILTER position, water travels from the pool, through the pump, down through the sand or DE media, and back to the pool through the return jets. The multiport valve position on WASTE changes that path entirely: water comes in from the pool, hits the valve, and gets routed directly out the waste port. It never enters the filter tank and it never comes back.
Two things follow from that routing. First, nothing is filtered. The valve’s internal diverter closes off the channel down into the tank, so the media is completely out of the circuit. Second, the pool loses water the entire time the pump runs, because every gallon the pump pulls in leaves through the waste line. Run a typical residential pump on WASTE and the pool drops 40 to 80 gallons per minute.
That is by design. WASTE, sometimes labeled DRAIN on the valve face, exists for the situations where you want water and whatever is suspended in it removed from the pool entirely rather than trapped in the filter. Our pool filter valve settings guide covers where WASTE sits alongside the other five or six positions on the dial.
Waste vs Backwash: Not the Same Thing
Waste and backwash are the two positions people mix up most, because both send water out the same waste line and both drop the pool level. The difference is what happens inside the filter tank.
On BACKWASH, the valve reverses the flow so water travels up through the filter media from the bottom. That reversed flow lifts the trapped dirt out of the sand or DE and carries it out the waste line. Backwash is a filter cleaning cycle: the whole point is that water moves through the media. The full procedure is in our guide on how to backwash a pool filter.
On WASTE, water never touches the media at all. The filter is not being cleaned, it is being skipped. You are simply pumping pool water overboard.
A quick rule of thumb: use BACKWASH when the filter is dirty, use WASTE when the pool is dirty with something you do not want inside the filter. The recirculate setting rounds out the trio of bypass positions, it also skips the media but returns the water to the pool instead of dumping it.
When to Use the Waste Setting
Vacuuming algae or heavy debris. This is the main event. Dead algae, flocculant sediment, and fine silt are exactly the wrong things to send through your filter. Dead algae clogs sand beds quickly, and the finest particles can pass straight through the media and blow back into the pool through the returns. Vacuuming on WASTE sends all of it out the waste line on a one way trip. If a green pool left you with a layer of dead algae on the floor after shocking, vacuum to waste first, then deep clean the media using our guide on how to clean a pool filter after algae.
Lowering the water level after heavy rain. A big storm can push the water line above the skimmer’s working range and dilute your chemistry. Set the valve to WASTE, run the pump until the level is back to the middle of the skimmer opening, and switch back to FILTER. It is faster and safer than draining with a siphon.
Partial draining. When you need to drop the level for winterizing, dilute very high stabilizer or calcium, or expose a tile line for repair, WASTE does the job with the equipment you already have. Never fully drain a pool this way without professional guidance, an empty inground shell can float or crack from ground pressure.
How to Vacuum a Pool to Waste Step by Step
Vacuuming to waste is a race against your own water level, so set everything up before the pump ever turns on.
- Turn the pump off and top up the pool. Add water until the level is near the top of the skimmer opening. Starting high buys you vacuuming time before the pump risks sucking air.
- Set the multiport valve to WASTE. Move the handle only with the pump off. Rotating a multiport valve under pressure chews up the spider gasket that seals each port.
- Connect and roll out the waste line. If your waste port is not hard plumbed, clamp on a backwash hose and run it somewhere that can take hundreds of gallons. Check local rules on discharging pool water.
- Prime the vacuum head and hose. Fill the vacuum hose with water at a return jet until the bubbles stop, then connect it to the skimmer or vacuum port. Air in the hose will drop the pump’s prime immediately on WASTE.
- Turn the pump on and vacuum quickly in sections. Work the worst debris first with slow, overlapping passes, but do not linger. If the water level approaches the bottom of the skimmer, stop and refill before finishing.
- Shut down, return the valve to FILTER, and refill. Pump off, valve back to FILTER, gear out, then refill and rebalance the chemistry.
If you normally vacuum on the FILTER setting and only switch to waste for heavy jobs, our walkthrough on how to vacuum a pool with a sand filter explains when each mode is the right call.
The Water Loss Warning
This deserves its own section because it catches almost everyone the first time. On WASTE, your pool is draining at full pump flow, roughly 40 to 80 gallons every minute. Twenty minutes of vacuuming can remove 800 to 1,600 gallons, which is 2 to 4 inches of water in a typical inground pool.
Two habits prevent trouble. First, top the pool up before you start, all the way to the top of the skimmer opening. Second, keep a garden hose running into the pool the entire time you vacuum. The hose will not keep pace with the pump, but it slows the drop and extends your working time. If the level falls below the skimmer while the pump is running, the pump sucks air, loses prime, and can overheat, so watch the water line as closely as you watch the debris.
Why Cartridge Filters Have No Waste Setting
The waste position is a feature of the multiport valve, and most cartridge systems do not have one. Cartridge filters are cleaned by opening the tank and rinsing the pleated element, not by reversing flow, so manufacturers plumb them with a simple two port design and no valve.
That leaves cartridge owners three workarounds when the pool needs a waste style vacuum. First, some cartridge pads are plumbed with a separate three way valve or a drain port downstream of the pump, which can serve the same purpose. Second, you can remove the filter tank’s drain plug and vacuum while water exits through the drain, messy but effective for small jobs. Third, and often easiest for a serious algae cleanup, use an independent tool like a submersible pump with a vacuum head attachment or a battery powered pool vacuum, so the debris never enters the circulation system at all. The techniques are covered in our guide on how to vacuum a pool with a cartridge filter.
Common Mistakes With the Waste Setting
Vacuuming algae on FILTER. The most expensive mistake on this list. Dead algae mats into sand beds and coats DE grids, and the finest particles recirculate right back into the pool. If the pool floor is green or gray, the valve belongs on WASTE.
Forgetting to move the valve back to FILTER. Leave the valve on WASTE after the job and the next time the pump kicks on, it quietly drains the pool. On a timer controlled pump this can dump thousands of gallons overnight. Make returning the handle to FILTER part of shutting down, every time.
Moving the valve with the pump running. True for every position, and worth repeating here because vacuuming involves several valve changes. Pressure against the diverter tears the spider gasket, and a torn gasket leaks water to waste even on FILTER.
Starting with a low water level. If you begin at mid skimmer, you may only get 10 minutes of vacuuming before the pump starts gulping air. Fill first, vacuum second.
Discharging where the water cannot go. Chlorinated water can kill lawns and plantings at high doses, and many municipalities restrict discharging pool water into storm drains. Point the backwash hose somewhere legal and drainable before the pump starts.
Related Guides
- Pool Filter Valve Settings Guide - every multiport position explained in depth
- What Does Recirculate Do on a Pool Filter - the other bypass setting and when to use it
- How to Backwash a Pool Filter - the full backwash and rinse sequence
- How to Vacuum a Pool With a Sand Filter - vacuuming on FILTER versus WASTE
- How to Vacuum a Pool With a Cartridge Filter - waste style vacuuming without a multiport valve
- How to Clean a Pool Filter After Algae - restoring the media after an algae cleanup
Frequently Asked Questions
What does the waste setting do on a pool filter?
What is the difference between waste and backwash?
When should I vacuum a pool to waste?
Why does my cartridge filter have no waste setting?
How much water do you lose vacuuming to waste?
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