Fuel Selector still draining in off position

[paul.j]

Hello all,

In the process of doing the annual on my 77' G model and were replacing the o-rings in the rear fuel strainer. The fuel selectors has been in the off position for nearly 18 months. The front strainer work was done with no issues. When beginning to work on the rear the fuel was still draining, after about 5 mins about 1 gallon had come out.

I saw an old post that indicated that there could be a check valve that could keep the shut off from shutting off. Any insight would be appreciated.