Fresh tank drain

I noticed after this last trip that my fresh tank had some water in it. Sounds like the check valve issue so I’ll try running the pump to see if that “fixes” it. I think it’s been that way for a while because I see spots on the inside that look like mold or mildew and there’s a faint water line around the bottom as well. Then I noticed that the drain outlet is far from the low point of the tanks. WTH sense does that make? I’ll need to disinfect, and flush, but it would be nice to be able simply drain it when there’s water in there. I don’t like the idea of running the pump to empty it because pumps don’t like sucking air. Any advice? How hard to add a drain at the low point, or would I be risking breaking it if on uneven terrain? Thanks in advance.