Problems with brake bleeder

I use a similar setup. Sounds like you need a gasket to seal the cap to the resevoir. If you can't find one the right size, check the plumbing section at the hardware store for sheets of rubber you can cut to size.

I'd guess it's similar to the 'Eazybleed' in the UK. This supplies extra caps in various sizes for different reservoirs and uses the spare wheel for air pressure. You have to be careful to not cross thread the caps and make sure all the pipes are a secure fit or fluid goes everywhere. But it works very well if you take care.

I'm attempting to do the same thing except I took a spare master cylinder cap and put a bicycle tube presta valve to it and pumped air into my master cylinder to create the pressure. Much cleaner than than the system you are trying to build. I also had air leaks sufficent to render it useless and am trying to resolve.

And yes I've also used the gravity feed system (one wheel at a time) and it did work. I am not positive that it would if you have a lot of dirt in your system.

For it to work, you'll need an air reservoir. The spare wheel is ideal for this. But reduce the pressure to about 15psi.

You can buy an anodized aluminum resovoir cap with a 1/4" NPT hole in it from ultimategarage.com. I got one for about $35 and installed a swivel fitting, an air regulator and gage.