Ditto Guys;
I had 4 OS 70 4 Strokes on my B-17. Bark you have it setup wrong! That is a vent fitting on the bottom of the OS 70FS not a pressure fitting, Use the muffler pressure just as you would on a normal 2 Stroke. Never store your engines Nose down If they are going to be in that position for a long time with no after-run oil in them. Plus it will make a mess in your shop dripping every so often. Fuel will separate and the Castor will just gum up the bearings and in time without a good cleaning can virtually sieze your bearings with Gunk.
Pull the plug and use some Marvel Mystery Air Tool oil or even ATF for your car and put a few drops in and spin it through lubing everything.
Then when your ready to fly, Fill the Tank and with the Plug removed Open the throttle and spin it through to get fuel through the system/engine. Now your ready to put the plug back in and your engine is clean.

Hope this helps.