I have a washing machine that drains through a pipe connected under the sink, before the U-bend. When it drains, bad smells come up through the sink. I want to give it its own U-bend, like my dishwasher already has, but the dishwasher's drain pipe just slides in the top of a 40mm waste pipe, and isn't sealed. I'm concerned it will still smell bad if I use this approach. Is there any reason I shouldn't seal the outlet pipe to the drain, before a U bend, to prevent any smells escaping? Alternatively, can I connect both appliances to the same U-bend, and seal their pipes onto it?