Heya Robbins...
I love that casino near your town! Anyway.. In upgrading the plumbing on one of my rigs (89 Sprinter), I used sikaflex marine sealant on all tank-to-fittings. No leaks with three years use. Sikaflex is a flexible, urethane based (moisture kicks it)sealant that does not harden. The putty Billy Mays pitches is an inflexible epoxy with good adhesive capability but limited - due to its nature, as a sealant. Also, be aware that your tank(s) and fittings may be of differing types of "plastic." If both are ABS, then perhaps an ABS glue would be appropriate. In my case the tank was polyethylene and the fittings were ABS.
As for the low pressure issue, perhaps the drain valves are partially open. Those valves are likely to be of the "gate" variety and without physically checking them, you cannot determine whether they are fully closed or partially open. I switched to Ball type valves. I can ID their status by simply looking at the position of the handle. If you have an accumulator tank inline, you might want to check the air pressure. Also check the voltage at the pump vs voltage at the auxiliary (house) battery. Dirty or corroded terminals/wiring can cause excess resistance and a subsequent voltage drop, resulting in a weak stream.
