Re: Ideas of things to hold water to drop motor into?
Something like this works fantastic well, install a spout on lower plastic barrel, connect a water hose to it and then to house drainage if that's ok with law regulations if any. While motor is on stand, pivot it fully, insert barrell, fill with water, once filled and engine is on, leave spout open while re filling with fresh water, will have colder water recirculating inside barrel with much better temp for engine. Once finished, empty barrel through hose, pivot engine fully again, release it from barrel.
Down issue, as there's always a down issue, with constant use barrel wall will be highly oil messed from combustion leftovers, worst if being a 2 strokes. Oily messy and not particular friendly to look or clean. After experiencing this filthy flushing method for some time and being a 2 stroke lover, muffs all the way.
You can even make a proper size box, place it under tail, flush engine on with muffs, all oily water drainage from engine will be discarded as same barrel example.
Happy Boating