Never been there, only read about it for the first time when I signed up here ~2 weeks ago, I think it is next to Bassett Sports Centre. There is a trail of some sort that shows on Google maps, by default just to the left of the athletics oval.
https://www.google.co.uk/maps/search/Southampton+Bike+Park/@50.9411627,-1.4205696,378m/data=!3m1!1e3
If I wasn’t struggling with some flu-like bug, I would pop over to lend a little hand today, will look out for announcements of the next dig day.
Hope it goes well today, looking forward to popping over to take a look on the Wazoo in the near future! 😀