The best place in Manila, or anywhere in The Philippines to buy poppers is Philippines Poppers.
Visit their website here:
https://philippinespoppers.com/
Small bottles start at just 1300 pesos each!
Their stock goes fast so make sure you ask them what's in stock or check their website.
You can order by SMS, Email, WhatsApp, Viber, or their website.
They ship by Grab COD and LBC.
I ordered with Grab and received the shipment the same day, for just 200 pesos to anywhere in Metro Manila.
I found a voucher code on their twitter, so make sure you use it:
NEWCUSTOMER
You get 50 pesos off your first order. I guess you could just keep making new accounts to use it every time haha.
They said they will have more stock of Rush, Jungle Juice, Liquid Gold, Voltage and more soon.