Washing machine drain non-return valve & connector
Initial context: We newly installed a dishwasher next to our washing machine some time ago, using a Y-connector to connect both machines' drain hoses to a single hose which in turn connects to the drain beneath the sink. However, the washing machine apparently lacks an inbuilt non-return valve, as the dishwasher's waste water finds its way into the drum whenever it drains.
I bought and installed a "Jepp Stop" valve, but it has proven inconsistently effective; it does seem to work sometimes, but other times the drum still fills up.
Searching for other non-return valve options brings up a number of results, and I'd rather not spend money and effort installing a new one without some assurance that it should work. Additionally, some of them have two "male" ends, suitable for connecting two hoses but not for connecting a hose to the Y-connector's also-"male" ends. If a "female"-"female" drain hose connector exists (apart from an entire extension hose) my search did not find it.
What kind of valve, if any, will be able to prevent backflow into the washing machine, and if such a connector would be needed, does it in fact exist?
Advice from 2 local tradespeople
Yes, a valve can help, but in the setup you described the better fix is usually to change the waste arrangement, not keep adding inline check valves.
What is happening is most likely backflow/back-pressure on the shared waste line. If both appliances are tied into one Y and then into a single hose, discharge from the dishwasher can be pushed toward the washing machine instead of cleanly into the trap. McAlpine’s appliance fittings are made specifically to avoid this kind of issue: they sell twin appliance connectors/traps for two machines, and also appliance connectors with an integrated non-return valve. Their inline non-return valve literature also says it “should only be used when there is no alternative,” which is a strong clue that correcting the pipework layout is preferred over relying on a flap valve in the hose.
So the order of preference is:
Best fix: replace the improvised Y-into-one-hose arrangement with a proper twin appliance trap / twin appliance waste connection under the sink. Those products are designed for a washing machine and dishwasher to share the sink waste correctly.
Next best: if you cannot change the trap, fit a purpose-made appliance connector with an integrated non-return valve on the branch that serves the washing machine. That is more promising than a generic inline valve because it is designed for appliance waste use.
Also check hose routing: dishwasher makers commonly require a high loop on the drain hose, and washing machine manuals commonly require the drain hose to terminate at a suitable height. If the hoses are too low, too deeply inserted, or sagging, siphoning/backflow gets easier.
On your connector question: yes, hose joiners/couplers do exist for appliance drain hoses, but they are usually sold as hose connectors/joiners rather than being described as “female-female” in plain language. Retailers do list appliance hose connectors for joining hoses, so that part is available if needed.
Fit a sink trap with two appliance spigots (or add a second standpipe) so dishwasher and washer drain separately.
• Make sure each hose has a high loop up under the worktop before dropping to the trap/standpipe.
• Inline check valves (Jepp Stop etc.) are often unreliable with appliance pumps/lint and can stick.
If you must keep a shared line, put the check valve on the dishwasher hose (arrow toward drain) and keep it accessible for cleaning — but expect it to be a maintenance item.
