APEX

I have a report,sql type that calls an item values to fetch and render rows.
The item is a multiple select list.Using the instr function as described in this thread
562795
It works fine with 'or' logical operator.But not the 'and' operator.

  Item ==> P10_PROD  

  Report Query ==>
      SELECT DISTINCT c_first_name,c_last_name,p_name
	 FROM V_CUST_PROD
	 WHERE (	      
                INSTR(':'||initcap(:P10_PROD)||':',':'||initcap(p_name)||':') != 0
                )

When user pick both Product1,Product2 from item P10_PROD,the report shows any customer with Product1 and/or Product2.

How can I retreive only customer with Product1 AND Product2 ? 

Thks for your advise.
Lam