Currently our church has a tithe fund where the pastor receives 85% as his salary. Should the pastor's tithe be put in here also?
That would be up to your church’s policy.
The issue with putting your pastor’s tithes back into the tithe fund is that they would be receiving 85% of it back again.
You might want to consider setting up a benevolence fund or a pastor’s discretionary fund up for their tithes.
Hope this helps.
P.S. Just a quick note, I do not know where you live, but if it is in the US, please be aware that sometimes the IRS considers the pastor receiving a percentage of a church's offering a private benefit. You might want to consult a knowledgeable CPA regarding this issue.