I have never had a fouled pipe. I think this is because I simply don't smoke enough to develop such problems on anything other than glacial timescales. I never smoke an individual pipe more than once a day and I rarely have more than 3 bowls. In fact, I usually only have one as I hate doing anything else (apart from drinking single malt) when I'm piping. This means I am often too busy to smoke a pipe. I always clean with pipe-cleaners until they emerge clean. If I have smoked a filter pipe (I never use the filters), I dismantle the pipe and throughly clean the stem and shank (mortise/tenon) with doubled-over cleaners. I have started to wait for half an hour or so to do anything to the bowl after getting rid of the dottle/ash/unsmoked tobacco, then I run my finger inside it, to "smear" the remaining ash around the bowl, to aid the cake. Before I smoke it again, I gently clean/bang the inside of the bowl; my reasoning is that anything which hasn't adhered overnight should not remain.
One cause for concern is that every single pipe I own has a nice cake on the top 2/3 of the bowl....and none on the bottom! I have decided to only smoke half-bowls for the next several months, to even this up, although the last half-bowl of EMP I had was decidedly sharp and juicy using this method.