While yes, there are no rules in effects order(sometimes happy accidents), there are certain placements that yield optimum results. In your case, a tuner should probably be first, or at least looped or diverted off sideways, so that it can receive the pure signal from your bass. Then, your compressor. The PT is an interesting choice; I have one in my guitar rig, very smooth and transparent. I use a Mark Bass Compressore for bass, but I'll check out the Piggy in that capacity. The reason for putting a compressor close to the beginning is to smooth out any dynamic volume fluctuation, and to expand any dead spots. A bass is a much more dynamic instrument than guitar, and in certain situations(AND used judiciously)it can fatten/sustain your notes while containing volume spikes. This is important if you're using any kind of octave device, which your Bass Whammy is. That should be immediately next. The Whammy would like to receive notes that have an even volume level and are sustained, so that it has signal that it can grab onto and processes with minimal glitching. If you eventually use any kind of envelope filter/auto wah, that would probably be next(with fuzz/distortion before IT perhaps, if you like the results)however, turn off the compressor if you engage an EF as it works against it. To function properly, an envelope filter is triggered by the very fluctuations in dynamic range(ie dramatic change in volume level)that a comp evens out. That being said, placing a comp at the end of your chain is probably not a good idea as the accumulated noise floor of all the pedals before will be "squeezed" up in volume. Also, the flavor of any preceding effect will be squeezed as well, unless that is a sound in particular that you're going after. For example, any time based modulation(flange, chorus, phaser)has a certain amount of volume fluctuation that is part of its distinct sound. Squishing it afterwords can diminish the effect somewhat.
