Don't really feel like they need scent.
Okay, so it looks like we're dropping scent.
I like Cleon's suggestion for the flung filth, too.
Something like this?
Flung Filth (Ex): A yahoo can fling a clump of its own filth as a splash weapon. Treat this as a ranged touch attack with a range increment of 10 feet. Any living creature (except yahoos and troglodytes) hit by the filth are sickened for 1d4 rounds (Reflex save for half duration), every creature within 5 feet of the point where the filth hits are sickened for 1 round by from the splash (Reflex save negates).
Hmm, I'm wondering whether a Fortitude save wouldn't make more sense, since that's what most sickened attacks use. We should probably add the 24 hour immunity and the poison save bonus too.
Revising...
Flung Filth (Ex): A yahoo can fling a clump of its own filth as a splash weapon. Treat this as a ranged touch attack with a range increment of 10 feet. Any living creature (except yahoos and troglodytes) hit by the filth are sickened for 1d4 rounds (DC X Fortitude save for half duration), every creature within 5 feet of the point where the filth hits are sickened for 1 round by from the splash (DC X Fortitude save negates). The save DC is Constitution-based.
Creatures that successfully save cannot be affected by the same troglodyte’s stench for 24 hours. A delay poison or neutralize poison spell removes the effect from the sickened creature. Creatures with immunity to poison are unaffected, and creatures resistant to poison receive their normal bonus on their saving throws.
Alternatively, we could allow the target to use either their Ref or Fort save.
Flung Filth (Ex): A yahoo can fling a clump of its own filth as a splash weapon. Treat this as a ranged touch attack with a range increment of 10 feet. Any living creature (except yahoos and troglodytes) hit by the filth are sickened for 1d4 rounds (save for half duration), every creature within 5 feet of the point where the filth hits are sickened for 1 round by from the splash (save negates). The target can make either a Reflex or Fortitude save, whichever is higher. The save DC is Constitution-based.
Creatures that successfully save cannot be affected by the same troglodyte’s stench for 24 hours. A delay poison or neutralize poison spell removes the effect from the sickened creature. Creatures with immunity to poison are unaffected, and creatures resistant to poison receive their normal bonus on their saving throws.
Hmm, I think I'm leaning towards the Fortitude save approach. The target's Dex is incorporated into their touch AC, after all.