SQL JOIN - 3 tables

Hi,
MS access / VB6/data report
I have 3 tables
t1 = products
t2 = purchases (related to t1(1 to many))
t3 = sales (related to t1(1 to many))
t2 & t3 are not related to each other
basically I want to build a profit report using SQL by products
and sums of t2 and t3
I have managed to get a satisfactory view using Right Outer Joins on both sales and purchases, however I am unable to bring them together so I get IE
prods sales purchases
prod1 300.00 250.00

I have tried but the resultant view multiples up sales and/or costs making the figures unacceptable

Any help would be appreciated