What would seal the best? (backplug for a tee piston)

[glass_05]

I am making a tee piston with a back plug to be taken out. On the back plug I am going to router out a groove for an o-ring. What I am wondering is what will make the best seal out of my 3 options.

1) router a groove so the o-ring sticks out a little and seals on the inside wall of the tee
2) have the groove deeper so the o-ring seals on the front face of the pipe inside the tee, and the plug actually fits into that pipe a little bit
3) make 2 different depth grooves. the o-ring will seal on the inside of the tee, and the plug will still fit inside of the pipe sealing on the font face of the pipe.

Here are some very very crude drawings I made quickly to explain what I mean. I should also note that if I do option 1, I do not make the groove deep enough to have the plug sleeve into the pipe, that is why with option 3 I need two grooves in order to make it sleeve and have the o-ring sealing on the tee.

[spudtyrrant]

the top one is the exact design i used for my 4" piston gun except mine sealed against the middle stop on a coupling it would be the best for the application it is very hard to router to an exact depth all the way around so i added teflon tape over the o-ring and put some silicon grease so it would be easier to slide in and it seals great

[cannon monkey]

XD i dont get it im confused now

[glass_05]

i have been practicing with the router and it is very consistent when i use the router table. i think i am going to try to do option 3, and seal the plug at 2 places for optimal results (I hope)