I was concerned about the same thing so I asked my URO. The infectious diseases department at Kaiser permente said there are a couple of concerns:
1: spread of the treatment vaccine into your partner
2: potential irritation of the urethra during sexual activity.
For this my doctor recommended no sexual contact for 48 hours-72 hours after treatment (usually didn't want to...) and for a week or so after no unprotected sex. Being that I am on 38 and my wife 36 and the potential for a 3rd kid still viable, they recommended we not try to get pregnant during the first 6 weeks after my last treatment.
I have seen a wide range of wait times from reliable online sources. It was also a question I had for my doc.
One week has been frequently been mentioned, along with many shorter times. and a few much longer times. My doc was good with one week. Like picking a number out of a hat.
This assumes, of course, that the bladder is running clean - clear, no blood, no debris - and things have settled down. It was more like a month after my first series of 6 before things stayed settled down; that was the point that the one week wait started.
I was super concerned about passing anything to my wife - a bit OCD perhaps. I wanted to make sure we were BOTH comfortable with the return to sex without a condom.
Google "BCG cancer sex" for a wide range of timing suggestions.
What's with this Bleeding ? 6/2015
DX: HG Papillary & CIS
3 Years and 30 BCG/BCG+Inf
Tis CIS comes back.
BC clear as of 5/17 !
RCC found in my one (only) kidney 10/17
Begin Chemo; Cisplatin and Gemzar
8/18 begin Chemo , round 3
Begin year 4 with cis