How to hook up a dishwasher drain hose under the sink
Connecting a dishwasher drain hose safely requires dealing with an under-sink outlet that powers the appliance while you are trying to test the setup. Uncertainty about the grey hose connection and proximity to electricity makes it difficult to verify the plumbing is right without creating a hazard.
What the numbers show
Counted from the threads quoted below. How we count
- Most of it landed at once — the busiest month was September 2026, with 7 people.
- This comes up 16.1× more often in r/Plumbing than across the site as a whole.
What people tried
Every workaround mentioned in the threads below. We haven’t tested any of them — and nobody here is claiming they worked.
Found another way around this?
Share your steps and trade-offs so fellow engineers don't have to reinvent the wheel. No account required.
- 1tightening a hose clamp on the discharge lineDid this help you?
- 2Raising the trapDid this help you?
- 3Using a dishwasher drain tailpiece in between the 90 and the teeDid this help you?
- 4Using a slip dishwasher tailpiece and cutting the pipe to fitDid this help you?
- 5Asking the contractor or builder for helpDid this help you?
- 6Prying open or cutting out the plastic knock-out plug with a utility knife and screwdriverDid this help you?
- 7Using a small rubber plug from a hardware storeDid this help you?
- 8Using a cork and electrical tapeDid this help you?
- 9Cutting the copper ring off with a Dremel, installing a short piece of PEX, crimping it, and using a PEX to flex hose adapterDid this help you?
- 10Replacing all the polybutylene plumbing in the entire houseDid this help you?
- 11Changing out the washer on the existing compression fittingDid this help you?
- 12Replacing the flare adapter with a 1/2 inch FIP by 3/8 compression adapterDid this help you?
- 13Removing the hose and brass adapter and taking pictures to the hardware storeDid this help you?
- 14Cut off the larger diameter section of the gray flexible hose end while leaving enough of the smaller gray flexible section to attach a pipe clamp.Did this help you?
- 15Placing the hose over the inner plastic piece so the clamp tightens around the rigid plastic instead of collapsing the rubber.Did this help you?
- 16Checking if an internal backflow flap is getting stuck when the clamp is overtightened.Did this help you?
- 17Checking if the sink connection nipple still has its knockout plug inside.Did this help you?
- 18Adding a new drain spot or replacing the sink tailpiece with a dishwasher branch tailpieceDid this help you?
In their words
Unedited, grouped by where they were said, most upvoted first within each place, each linked to the thread it came from.
“Where do I put the washer drain hose? The cap at the top twists off but I dont think that’s where I should insert the drain hose. Shouldn’t it go downward? The bottom cap won’t twist open.”source ↗
“I just moved to a new apartment and this is looking kind of sketchy if im honest. The grey hose is the dishwasher.”source ↗
“Ok so it’s the bottom plug. There no way to twist it without breaking it? Also what’s up with that top plug that I can actually twist open?”source ↗
“I just recently moved into a new place and discovered the hard way that our dishwasher wasn't connected properly to the drain.”source ↗
“I would try it out, but I am a bit concerned about the outlet behind my sink. It is connected to the dishwasher, so I can't test the connection while it's off.”source ↗
“Hello, I’m looking for some advice on adding a dishwasher drain under my sink.”source ↗
“There is very little room vertically from the bottom of the sink to the wall drain.”source ↗
“Does the inlet need to be capped off if it isn't getting reconnected to the dishwasher?”source ↗
“I just bought a new dishwasher and doing the install at the moment. I removed the kick plate, and realized that the supply line is a Poly B pipe. If I were to change it to a braided line, what would be the best and easiest way to tackle this?”source ↗
“My main issue is using the existing compression fitting that's at least 30 years old.”source ↗
“I don't now where to terminate my dishwasher hose (last picture) into. What do I need to change/buy?”source ↗
“I have older pipes and I went to connect my dishwasher and the line was too small, so I got a 3/8x1/2 adapter which fit the ½ side (the larger pipe) but the dishwasher supply line is still too small to fit in that. What am I missing?”source ↗
“This is the dishwasher drain line. Was going to hook it up to the air gap but it doesn't seem to go on far enough because the bigger part is hitting the T splitting towards the garbage disposal. Would I be making a mistake to cut the larger section shorter?”source ↗
“Problem is when u hook up that drain hose with a clamp, if I tighten it too tight, water doesn't drain. If it's too loose the water leaks, anyone know what I'm doing wrong?”source ↗
Where this came up
People with this problem also raised
- 2How to connect an RO drain to a garbage disposal
- 3Washing machine drain pipe keeps leaking after putting back on
- 3Portable washing machine hose doesn't fit kitchen faucet
- 14Where do I run the vent for a washer installation?
- 14How to connect a sink drain to existing glued PVC pipes
- 5Bosch dishwasher leaking from pump and gasket