@Waffle Of War: As people have said, diamond pipes are good. They attempt to send the designated item down the designated path, but if the inventory is full they'll send it down a blank path. You could also consider Redpower tubes. They always fill the closest inventory first and never overflow, but they can be a bit fiddly in how they connect to some of the forestry machines with multiple input slots. Whether you go for BC pipes or RP tubes, though, you should really get an overflow chest. That tends to solve a lot of the overflow problems.
As for engines, stirling engines (frankly, any engine other than combustion) won't explode unless you're doing something very stupid. If you absolutely must avoid even the faintest possibility of explosion I recommend a Thermal Expansion Steam Engine. Instead of exploding it will overheat and freeze up until you hit it with a wrench. It requires water, but it gives you twice as much power as a stirling engine. You should also consider a Railcraft Hobbyist steam engine - they give you the most energy per coal out of the basic engines (though it only outputs at 1.6MJ/t) and will only explode if you let it run dry and then try to add water while its still hot. Like the thermal expansion engines if you just let it keep running without somewhere to dump the energy it will simply freeze up, you have to go out of your way to make it explode.
To get mulch from a squeezer to a fermenter, use a wooden pipe with a redstone engine. It's the same process as getting the apple juice out, except the juice uses a waterproof wooden pipe. Forestry machines are actually quite intelligent about taking inputs from BC pipes, so you can route the mulch to any side of the fermenter and it will end up in the correct slot.
