The quenched site-diluted spin- 5 2 Blume-Capel model is studied using a new technique in effective field theory that employs a probability distribution within the framework of single-site cluster theory based on the use of exact Ising spin identities. The probability distribution, derived with the aid of Tucker's generalised Van der Waerden operators, correctly account for the single site kinematic relations and certain configurational averaging identities. The concentration dependence of the ferromagnetic phase boundary is studied. In particular, it is found that a range of single-ion field strengths exists over which the critical concentration for ordering varies anomalously. Results for the honeycomb, square and cubic lattices are presented. The thermal variation of the magnetization, the quadrupolar, and higher order magnetization moments, are presented for selected values of the concentration.