North of north docks, on the small landmass that juts out above the docks on the map.They are sitting on top of a small box, next to a red toolbox. West of the north docks, close to the ocean If you do the cutting torch first it changes to optional. I was wondering wtf the charges were for as I always use drainage. Then I found out you don't need them. Yuskus1234. • 3 yr. ago. You can either do cutting torch or explosives, they both say mandatory but you only need to get 1. [deleted] OP • 3 yr. ago. There's only one guard patrolling there so it's very easy to get out undetected. Head south and swing by the south side of the compound. You don't even have to leave the boat, just drive over the general area and the notification that you've scoped the drainage tunnel should pop up. Pavel will mention it as well. A quick tutorial to show you exactly How and Where to find the Drainage Tunnel In the GTA 5 Perico Heist! The Zancudo River is a river located in Blaine County, San Andreas that appears in Grand Theft Auto V and Grand Theft Auto Online. The river runs east-west from its source at the Alamo Sea to its mouth at Lago Zancudo. At its eastern end, it is narrow and forms several sections of rapids and minor waterfalls, while at its western end, it forms a wide river delta with a large swamp. It is rEXLVd.