What I did - I had a 50/50
juice I really wanted to
vape in cartos but I know even 30% VG causes my cartos to clog up sooner and performance to degrade faster. So I bought a 100% PG
juice in the same nicotine level and a similar flavor and I cut it with that. Not the same flavor exactly but at least it vapes nicely in the carto and gets me decent reuse of the carto.
The substances listed in the answer above will thin it better with less added. What I do requires more be added but preserves the nicotine level and keeps a similar flavor.
If you have a fat battery model (450mah+) somebody said those dual coil (LR) cartos work well with VG