I've never used those water bottle fuel tanks, so I have no experience with the flexible / pumping influence those bottles may have on a exhaust pressurized fuel tank system... Those tanks work well with the pumper / diaphragm carbs, due to the tank being vented to the atmosphere... I never liked the screw on cap, so I always opted for the rigid poly tanks that use the expanded rubber stoppers... I measured the orifice of the pressure fitting in the muffler for the OS boxer and the orifice ID is .078", same as on the saito FA130TD... too small of an orifice will cause a latency in the back and forth exhaust pressure pulse to the tank,