I'm building a custom loop and don't want to run my reservoir over my components for aesthetic reasons and what I'm wondering is would it be ok to have just the one tube connected to a splitter which is connected to the pump and the return from the rest of the loop and forego the return to the reservoir
If I understood what you explained right...
You want to take a closed loop, with no res, add a splitter before the pump and use the additional port to put the res in there. So your res will not be a flow through part of the loop, it will be just a res sitting there to keep the loop full.
If that's what it is, you must consider at least two different forces: gravity and water pressure. For a setup like that to work, the res must be at the highest level and always before the pump.
M
