Thinking about purchasing a 4x4 flood tabel to upgrade from my hd mortar tray. I have wanted one for a while!!!. ANyway. . . How many gallons do i need to put on the table. I only want to flood a few inches up. I use rockwool. I wondering if the whole table will need like 10 gallons? Just hoping i could use a rubbermaid 25 gallon roughneck as a reservoir. Use a cardtable with a whole drilled in it and the legs chopped as a cheap stand. Fig i could load say 15 gallons in a roughneck safely maybe more, tho dont want to risk it.