I have an external double socket - in a sealed box - to run a filter and a water pump for the fountain for my pond. Each is wired to a separate plug. I've just been told I need to add an air stone, but now don't have enough plugs and there's no room in the external box for a multi plug. Can I just wire both the air stone cable and the filter cable into one plug - they would both be on at the same time anyway - I'm sure I've seen this in the past for lamps, but guess it's not best practice. Otherwise, does anyone have any suggestions? Thanks