Why does my mouthpiece do that? Somtimes it's so bad, that I lose my embrochure and miss notes. Also if I sit my trumpet down, spit will also come out.

There is spit in the horn, gravity takes care of the rest. The only solution is not to play. Every breath that you exhale has moisture in it. Breathing into a horn moves that moisture forward where it can condense. Articulation blows minute amount of spit. It comes with the territory!

Where is it coming out of the mouthpiece? if it's from the cup, my horn does that when I lay it on it's side for a while. I just wipe it off with a cloth.

Ummm.. tilt your horn down and gravity will do the rest.

What if you in say, marching band? I must hold my trumpet above parallel with the ground. The water is coming back out of my mouthpiece after a few seconds of playing like a waterfall... and its hard to keep playing. When I pull my mouthpiece out and blow, some drainage comes out.. this doesn't happen to most of the other trumpet players.... whats wrong? I think its my mouthpiece, I use a Bach 3C.

Tilt it down and use the spit valve to empty it. It is not the mouthpiece.

If I played the trumpet pointing up all the time, we would all have the same problem as you.
Tilt it down occasionally and empty it. If you hear a crackle you are not emptying enough.

cant do that while marching..... and im at attention most of the time

The thing is, backwash only happens with me and not the other trumpet players. We all hold our trumpets above parallel.

Originally Posted by miketseng

The thing is, backwash only happens with me and not the other trumpet players. We all hold our trumpets above parallel.

Condensation can be linked to temperature and humidity. I know if I played with my horn pointing up ALL the time I too would have your problem in a cold wet environment. Tilt it down and drain the spit. Condensation is normal. It is not all spit from your mouth.

In any case the mouthpiece is not creating the moisture, it is the blowing of warm air from your body into a cold piece of metal. The spit valves are there to drain the moisture. That only works if you tilt the horn down to allow it to run to the valve.

Speak to your fellow members in the band, they are all draining the moisture by tilting the bell. (They probably know the routine well, and when is the right time to empty the water).