The problem

I am installing a new Bosch dishwasher and have run into a conundrum hooking up the drain. The parameters are the following:

  • The dishwasher drain hose has a rubber bit on the end marked 1/2" and 3/4". It steps directly from 3/4" to 1/2" without an intermediate 5/8" level. The dishwasher is otherwise completely installed, so I would prefer not to pull it out to put on an entirely new hose.
  • The air gap has a 5/8" inlet and 7/8" outlet.
  • I want to drain into a garbage disposal with a 1" inlet.

This leads to two problems:

  • The drain hose appears not to fit the air gap inlet. I suspect I could jam it onto the air gap inlet with enough force, but I'm worried about longevity.

    I do not mind replacing the air gap, but I've been unable to find one that had a 1/2" or 3/4" inlet and 1" outlet. Everything I've found, both locally and on the Internet, has 5/8" inlet and 7/8" outlet.

  • I need some way to connect the air gap outlet to the differently sized inlet on the disposal or (less preferred) some other part of the drain under the sink. I only need a couple of feet of hose.

The previous dishwasher had no air gap at all; it connected directly to the disposal (which led to at least one adventure I'd rather not repeat).

Right now I've taped the hose to drain into the sink, so do I have some time to do it right.

I'm puzzled because this seems like a common situation, so I wonder what I'm missing.


Here is the situation. The red arrows are the two connections I am trying to make.



End of dishwasher hose:


Air gap:

air gap

Disposal inlet (the rag is simply to prevent leakage so we can use it while I solve this hookup problem):


  • I've never needed one, what happens if you don't have an air gap?
    – Mazura
    Commented Nov 24, 2014 at 23:10
  • 1
    @Mazura an airgap helps prevent backflow of contaminated water into the supply in the unlikely event of pressure inversion in the pipes.
    – Matthew
    Commented Nov 25, 2014 at 0:54
  • @Mazura, I've drained the sink into the dishwasher at least twice; both times it happened when the disposal clogged and the water level in the sink went above the maximum height of the dishwasher drain hose. An air gap would have prevented this (as would paying better attention, but everyone has such lapses from time to time).
    – Reid
    Commented Nov 25, 2014 at 15:38
  • A short chunk of 3/4" OD 1/16" wall tubing slipped inside the 3/4 section should make 5/8" perfectly.
    – Ecnerwal
    Commented Feb 7, 2017 at 2:42

2 Answers 2


I have had my Bosch dishwasher for about a year using the same setup you contemplate, so I'm familiar with the exact drain connector you have on the dishwasher hose. On mine, there was something of a taper between the 1/2 and 3/4 section and being rather flexible rubber, and I had no difficulty stretching the 1/2 section of the fitting to fit on the 5/8 gap fitting. I then tightened down the hose clamp with a hex bit on my cordless driver. The clamp was tight enough to somewhat compress a groove into the rubber, and I tugged on the thing as hard as I could. It isn't coming off IMHO. I'm at work, but can send a picture later if you need.

I understand you are worried somewhat about the quality of the connection. You could get a 1/2 to 5/8 adapter like this:

enter image description here

But that would entail 3 hose clamps and a section of 5/8 ID hose to connect between the adapter and air gap. That seems like more points of failure. At any rate, I think you already have what you need to get this working.

  • Thank you Bob. Are you concerned about excess stretch in the 1/2-over-5/8 connection having poor durability? Re. "you already have what you need" (always my favorite answer), were you intending that to apply to the 7/8" outflow to 1" disposal inlet as well? If so, I don't quite follow.
    – Reid
    Commented Nov 25, 2014 at 15:40

Best thought I've got is to get a couple of tubing size adapters, and additional pieces of tubing if necessary, so everything's connecting to a matching size.

Note that if a hose is a bit too large, a hose clamp may compress it enough to get an adequate seal.

  • Thank you. Would you consider 1/8" over to be "a bit too large" but in the compressible range?
    – Reid
    Commented Nov 25, 2014 at 15:43

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.