An assembly for delivery of treatment fluid at a target location downhole. The assembly is configured to avoid any substantial loss of treatment fluid in advance of reaching the target location in spite of low well pressure or a potentially excessive depth of the location. The assembly also allows for loading with treatment fluid from a downhole end thereof so as to avoid driving treatment fluid through the entirety of a tubular accommodating the assembly. The assembly may employ a spot valve to enhance filling with treatment fluid along with a backpressure valve coupled to the spot valve on-site so as to avoid premature loss of treatment fluid during a delivery application.